Many processes used in modern integrated circuit fabrication tend to introduce undesirable sodium ions into the integrated circuits which ultimately are formed. For example, processes which utilize photoresist or etchback techniques are typically abundant sources of mobile sodium ions. The mobile sodium ions, once introduced, tend to migrate through the integrated circuit and ultimately degrade circuit performance.
Various doped glass layers are often introduced into integrated circuits by designers to getter sodium ions. Typically, boron and phosphorus dopants are introduced into silicon dioxide layers. The doped silicon dioxide layer tends to attract and hold the sodium ions, thereby preventing them from migrating through the integrated circuit. Thus, the undesirable sodium ions are more or less chemically trapped within doped glass layers within the integrated circuit where they can, hopefully, do no harm elsewhere.
Nevertheless, there remains a continuing need for better methods of dealing with the presence of sodium ions in integrated circuits.